An important interface between different types of systems is a connection between analog and digital parts of the systems. In order to correctly convert the signals on this connection, A/D and/or D/A converters are required.
In the case of many types of A/D and D/A converters, reference elements are needed which derive further variables, and for the A/D and/or D/A conversion from a pre-set reference variable, such as a reference voltage. These reference elements form a weighted network and are designated as weights as described below. In practice, the weighted networks are implemented, for example, with resistors, transistors or capacitors. Such A/D converters work, for example, according to the successive approximation methods. A converter with charge distribution (and redistribution) can be taken as a representative example, in which case the weighted network consists of capacitances. Weighted resistance networks are used, for example, in converters based upon method of weighted currents or with a ladder network (R-2R). Since the weights serve as a reference for the conversion, it is important that the weight values, for example the capacitor values, relate to one another in an accurate pre-set ratio. However, problems can result because the weights cannot be manufactured with sufficient accuracy.
Therefore a calibration of the weighted network is necessary. A possible solution for this is self-calibration, for example, is described in EP 0320642 B1.